As the characteristics of CMOS (Complementary Metal-Oxide-Semiconductor) image sensors, CCD (Charge Coupled Device) image sensors, and other image input sensors have improved, the demand for them in applications such as digital cameras and camera-equipped cell phones has increased.
There is a need for further improvement of the characteristics of said image sensors, such as an expansion of their dynamic range.
For example, Japanese Kokai Patent Application No. 2003-134396, Japanese Kokai Patent Application No. 2000-165754, Japanese Kokai Patent Application No. 2002-77737 and Japanese Kokai Patent Application No. Hei 5[1993]-90556 have disclosed solid-state image pickup devices that have realized a wider dynamic range. In these solid-state image pickup devices, however, it is difficult to realize a wider dynamic range while maintaining a high sensitivity and a high S/N ratio. In order to solve this problem, Patent Reference 5 has disclosed a type of solid-state image pickup device.
The solid-state image pickup device described in Japanese Kokai Patent Application No. 2005-328493 is structured such that the photoelectric charge overflowing from the photodiode of each pixel is accumulated in the floating diffusion and electrostatic capacitive element. The signal for each pixel is obtained from the photo-electrons in the diode when the photo-electrons do not overflow, or by both the photo-electrons in the photodiode and the photodiodes overflowing from the photodiode when said photo-electrons overflow from the photodiode.
However, when the solid-state image pickup device described in Japanese Kokai Patent Application No. 2005-328493 is manufactured in a CMOS process, the dark current component with respect to the photo-electrons overflowing from the photodiode increases by 3-4 orders of magnitude over the desired level. This is undesirable for use in accumulating photoelectric charge over a long time, and there is a need to suppress this phenomenon. The sites for generation of the dark current component include the interface immediately below the gate of the transistor, the side surface of the element separating insulating film, the portion in touch with the depletion layer on the silicon surface, etc.
A general object of the invention is to address the difficulty of suppressing the dark current component with respect to the photo-electrons overflowing from photodiode in a solid-state image pickup device with a wide dynamic range.